1. Field of the Invention
The present invention relates to an outer tube for a front fork.
2. Description of the Related Art
As an outer tube for a front fork, as described in Japanese Unexamined Patent Publication No. 2009-180293 (patent document 1), there is an element structured such that a metal upper collar to which an upper vehicle body attaching bracket is connected is fitted and attached to an upper end portion of a fiber reinforced plastic (hereinafter, refer to as FRP) pipe, a metal lower collar to which a lower vehicle body attaching bracket is connected is fitted and attached to an intermediate portion of the FRP pipe, and a metal seal case for inserting and supporting an inner tube is fitted and attached to a lower end portion of the FRP pipe, for reinforcing the FRP pipe.
In this case, the upper collar and the seal case are brought into contact with an upper end surface and a lower end surface of the FRP pipe, and is adhered to the FRP pipe. On the other hand, the lower collar is adhered after being positioned to an appropriate position of the intermediate portion of the FRP pipe.
The following problems exist in the outer tube for the front fork in accordance with the related art.
(1) It is necessary to set the position of the lower collar and it takes a lot of effort, at a time of adhering the lower collar to the intermediate portion of the FRP pipe.
(2) In the case that the FRP pipe is used in the outer tube for the front fork of the vehicle, a load which acts in a vehicle body back and forth direction and a vehicle body right and left direction of the front fork generates a stress concentration in a contact portion with a lower end edge of the lower collar in the FRP pipe, and makes the FRP pipe disadvantageous regarding fatigue strength.
(3) In the case that the FRP pipe is used in the outer tube for the front fork of the vehicle, it is necessary to appropriately change a fiber direction of the FRP in each of laminated sheet-like raw materials or partly change the number of lamination, at a time of manufacturing the FRP pipe. This is done by laminating the sheet-like raw materials such as a one direction material, a cross material or the like of the FRP, in the case that it is intended to appropriately change a bending stiffness of the outer tube with respect to the vehicle body back and forth direction and the vehicle body right and left direction of the front fork in a pipe circumferential direction, which takes a lot of effort.